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Statically indeterminate truss

  1. Oct 25, 2013 #1
    1. The problem statement, all variables and given/known data
    Calculate the member forces in the statically indeterminate truss. Member AF and BE is not connected at the intersecting point. The cross sectional area is the same for all the members.

    Illustration of truss:https://www.dropbox.com/s/xuvwdpybn3ajp9o/problem truss.jpg

    2. Relevant equations
    I first calculate member AF using the unit load method. When I know AF I have an statically determinate truss and I then use the joint method and the equations of equilibrium to find the other member forces.

    3. The attempt at a solution
    I calculated the following member forces. Does this look correct?
    AF = 44 kN
    CF = 125 kN
    BC = -75 kN
    FB = -135.2 kN
    FE = 48.6 kN
    EB = -81 kN
    EA = 64.8 kN
    AB = -26.4 kN
  2. jcsd
  3. Oct 26, 2013 #2


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    raymanmusic: Excellent work. All of your answers are currently correct. The only minor problem is, you should list all answers to at least three significant digits, not two significant digits. Therefore, the member force for members AF, CF, BC, and EB should instead be AF = 44.0 kN, CF = 125.0 kN, BC = -75.0 kN, and EB = -81.0 kN. We have no way of knowing that the digit you rounded off just so happened to be zero, for all four of these members.

    (1) Generally always maintain at least four significant digits throughout all your intermediate calculations, then round only the final answer to three significant digits (unless the first significant digit of the final answer is 1, in which case round the final answer to four significant digits).
  4. Oct 26, 2013 #3
    Thanks nvn! Yes, sorry the member forces AF, CF, BC and EB are rounded off to zero as you say.
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